Right, I just died to a time Skitter that dealt about 10-15 points of damage through armour, so I'm here to hand out some sweet, sweet advice candy!
If an item isn't auto-gathered, you need to dig it up with a sharpened item or shovel. You can do this on water to yield sand, on snow to yield a pile of snow, on bogs to yield peat and vines, on other terrains for piles of dirt. If you dig down past the top layer, you may well find clay. Red spotted mushrooms hurt you in addition to feeding you. Be careful.
Lighting a fire is one of the most basic, and yet most difficult parts of the game. You need 5 rock-like items and 1 fuel-like type. doesn't matter whether the fuel is logs, coal or peat. Kindling and twigs, despite giving fuel, are NOT fuel-like items, and won't work. Once you've built the campfire, right click it to put it down. Now use a fire plough or hand drill to set it aflame. Boom.
You pick up corpses by double clicking a sharpened object when you're facing (not on top of) the corpse. Spiders give nothing, but carving a couple of times will clear the land so you can put down objects.
As for the furnace, that's in my latest list update, I still have no idea how to make a forge and anvil, though. No amount of rocks appears to work, no amount of rope-like, rope, string-like, string, pole-like or wooden pole will work together to make it.
Incidentally, I still can't find a use for rope. No matter how I put things together, how many of everything I have, it won't do anything. Don't make it, as it uses up 1 weight, without having any use.